Ion generator comprising a shielded radioactive source and means for forcing air past the radioactive source



M y 1965 w. Y. FISH ET AL 3,182,194 ION GENERATOR COMPRISING A SHIELDED RADIOACTIVE SOURCE AND MEANS FOR FORCING AIR PAST THE RADIOACTIVE SOURCE Fild Dec. 8," 1960 3 Sheets-Sheet l Manual. fiarf/ May 4, 1965 w. Y. FISH ETAL 3,182,194 ION GENERATOR COMPRISING A SHIELDED RADIOACTIVE SOURCE AND MEANS FOR FORCING AIR PAST THE RADIOACTIVE SOURCE 3 Sheets-Sheet 2 Filed Dec. 8, 1960 F I I5 E INVENTOR8 Wa/fer X 55% M///a/27 ,4 (m/9e,

y 1965 w. Y. FISH ETAL 3,182,194

ION GENERATOR COMPRISING A SHIELDED RADIOACTIVE SOURCE AND MEANS FOR' FORCING AIR PAST THE RADIOACTIVE SOURCE 3 Sheets-Sheet 3 Filed Dec. 8. 1960 FlE 4- INVENTORS h/a/fer 1 55/2. /1 ////a//7 A! m/eg/n 8y The 7745A. Mad/4%."

4rra g firs' FIE E United States Patent ION GENERATOR COMPRISING A SHIELDED RADIOACTIVE SOURCE AND MEANS FOR FORCING AIR PAST THE RADIOACTIVE SOURCE Walter Y. Fish, William H. Conlee, Jr., and Thomas L.

Martin, Jr., Tucson, Ariz., assignors, by mesne assignments, to Wesix Electric Heater Co., San Francisco, Calif., 21 corporation of California Filed Dec. 8, 1960, Ser. No. 74,608 15 Claims. (Cl. 250-44) This invention relates to an ion generator and method and more particularly to an ion generator and method for using a radioactive source having relatively high activity levels.

In many commercial applications, there is a need for an ion generator for creating large quantities of ions of one sign to eliminate static charges of electricity. Heretofore, considerable work has been done in the production of ions of one sign as disclosed in United States Let ters Patent 2,576,399; 2,589,613; 2,594,777; 2,639,972; 2,640,158; 2,654,017; 2,928,941; 2,928,942; 2,785,312; and 2,850,641.

The use of high energy radiation such as from hard beta and gamma sources for the production of unipolar ions has been relatively limited because of the creation of undesirable secondary gamma radiation and the scattering of hard beta and gamma rays into areas where they constitute a radiation exposure problem. The range of hard beta rays in air has made it dimcult to construct practical ion or plasma chambers because of the large and cumbersome size normally required. It is for this reason that attempts heretofore made to utilize such high energy radioactive particles in ion generating devices has resulted in devices which have either too low an ionization level to be effective with an inefiicient use of the ra dioactive material, or an expensive device which was so bulky and cumbersome that it was of no practical use. There is, therefore, a need for a new and improved ion generating device for generating ions of one quantities so that the device would be suitable for many industrial applications requiring large quantities of ions as, for example, the elimination of static charges.

In general, it is an object of the present invention to provide an ion generator and method which will make possible the generation of large quantities of ions of one sign without creating radiation exposure hazards.

Another object of the invention is to provide an ion generator and method of the above character in which high energy radiation is utilized.

Another object of the invention is to provide an ion generator and method of the above character which utilizes the radiation from high energy radioactive sources effectively.

Another object of the invention is to provide an ion generator and method of the above character in which secondary radiation is minimized.

Another object of the invention is to provide an ion generator and method of the-above character in which back scatter of the rays from the radioactive source is utilized to cause the production of large quantities of ions of both signs in air.

Another object of the invention is to provide an ion generator and method of the above character in which the escape of radiation from the radioactive source is minimized.

Another object of the invention is to provide an ion generator and method of the above character in which the air flow through the generator is substantially unimpeded.

Another object of the invention is to provide an ion sign in large generator and method of the above character in which the undesired ions are efficiently separated from the desired ions.

Another object of the invention is to provide an ion generator and method of the above character in which a member of high density material is spaced from the radioactive source and is arranged to provide substantial back-scattering of the radiation from the radioactive source.

Another object of the invention is to provide an ion generator of the above character in which an additional member of low density material is provided to prevent or inhibit secondary radiation.

Another object of the invention is to provide apparatus of the above character in which means is provided for shielding the radioactive source.

Another object of the invention is to provide an ion generator of the above character in which the shields introduce minimum turbulence into the air stream.

Another object of the invention is to provide an ion generator of the above character in which radiation shields or traps are utilized.

Another object of the invention is to provide an ion generator of the above character in which the means for introducing air fiow into the ion generator includes means for inhibiting the escape of radiation.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1 is a perspective view of an ion generator incorporating our invention.

FIGURE 2 is a side elevational view, with certain parts broken away, showing a portion of our ion generator.

FIGURE 3 is a cross-sectional View taken along the line 3-3 of FIGURE 2.

FIGURE 4 is a schematic diagram showing the fields created between the two electrodes.

FIGURE 5 is a view showing the operation of the beta trap.

FIGURE 6 is an isometric view of another ion generator incorporating our invention.

In general, our ion generator consists of a member of low density material having open ends which surround a member of high density material also having open ends. A radioactive source emitting rays having high energy levels is mounted within the member of high density material. The spacing between the radioactive source and the member of high density material is such that it is less than the normal distance of travel of the radioactive rays in air so that the rays impinge upon the member of high density material to cause back-scattering of the rays, or in other words, to cause the rays to be reflected back and fourth from one surface of high density material to another to create large quantities of positive and negative ions within the air space enciosed by the member of high density material. Positive and negative charges are applied to the high and low density members to establish an electrostatic field between the members for separating the undesired ions from the desired ions. The ion generator is shielded in such a manner that it is not a radiation hazard, and still at the same time produces large quantities of ions or" the desired sign at relatively low cost.

Our ion generator, as shown particularly in FIGURES l3, consists of a carrying case 11 which houses a power supply 12 and which is provided with a space 13 for receiving the ion generating assembly 14. The ion generating assembly 14 is shown in detail in FIGURES 2 and 3 and, as shown, consists of an outer open ended tubular member 16 which is formed of a material of relatively low density such as aluminum. By low density, we mean a material having an atomic number of 25 or less. The outer tubular iiember 16 is supported in a suitable manner such as by a pair of wooden stands 1'7 mounted on the underside of the tubular member 15.

An inner open ended tubular member 18 is mounted within the outer tubular member 16. The inner tubular member 18 has an outside diameter which is substantially less than the inner diameter of the outer tubular member. The inner tubular member also has a length which is substantially less than that of the outer tubular member for a purpose hereinafter described. The inner tubular member is formed of a material having a relatively high density such as lead. By high density material, we mean a material having an atomic number above 25. The inner tubular member 13 is supported within the outer tubular member 16 by pairs of supporting members or posts 19 of suitable insulating material such as plastic which are held in place by screws 21 threaded into the posts 19 from the outer tubular member 16 and from the inner tubular member 18.

A radioactive source 23 is mounted within the inner tubular member 18 and can be any suitable form. For example, as shown in FIGURE 2, it can be in the form of Krypton-85 (Kr 85) source. Since Kr 85 is a gas, it is enclosed within a suitable sealed structure such as a thin metal tube 24- of aluminum or other low density material which has been sealed off at its ends by plugs 25.

The radioactive source 23 is supported by a pair of arms 27 mounted upon a block 28 of suitable insulating material such as Plexiglas. The block 28 is secured to the inner tubular member 18 so that the axis of the tubular radioactive source 23 is substantially in line or coincident with the axis of the inner tubular member 18.

A pair of shields 31 is provided on the opposite ends of the radioactive source 23 and, as shown, is in the form of cones with the pointed ends facing towards the open ends of the tubular member 18 to reduce the turbulence of the air within the member 18 as hereinafter described. The conical shields 31 are formed of any suitable low density material such as aluminum. They are mounted on the outer ends of the radioactive source 23 and are supported by the arms 27.

Means is provided for introducing a flow of air through the inner tubular member 18 and between the outer tubular member 16 and the inner tubular member 18. This means for introducing air can be in the form of a separate source of compressed air connected to the outer member 16 by a hose, or it can be in the form of a fan 33 mounted in one end of the outer tubular member 16 and serving to cause air to flow from right to left as viewed in FIGURE 2. The fan is driven by a motor 34 with a configuration such that it impedes the flow of air through the outer tubular member 16 as little as possible. 7

The fan 33 is provided with a plurality of blades 36 which are formed in a particular manner as shown particularly in FIGURES 2 and 3 so that they overlap and so that they travel in relatively close proximity to the inner surface of the outer tubular member 16. The fan blades 36 are formed of a suitable material of 'low density such as aluminum or plastic to minimize secof the inner tubular member 18. It is formed of a suit- 1 able material such as plastic. The material is preferably,

though it need not necessarily be, a nonconductor to minimize secondary radiation and/or electron emission.

The insulating plug forming radiation trap 46 is formed of a substantial thickness t. It is provided with a plurality of holes 47 which are drilled into the plastic and extend in a direction which is parallel to the longitudinal axis of the inner tubular member 18. The holes are of a predetermined diameter d and are spaced over the entire surface of the insulating plug or shield 45. The holes as hereinafter described are provided to permit the passage of air through the inner tubular member 18 and still at the same time prevent the escape of radiation from the tubular member 18. The design of this plug is shown in FIGURE 5. The basic design of this parameter d/t, as shown in FIGURE 5, is controlled by the minimum angle of incidence 0. This included angle 0 can include only that radiant flux which after passing through the hole produces a radiation level which is satisfactory in accordance with licensing requirements of certain governmental agencies as, for example, the Atomic Energy Commission. In designing the radiation trap, it is also desirable to select the proper ratio of A/O, wherein A is equal to solid area and O is equal to open area of holes. This ratio is selected to achieve the maximum ion output while yet keeping the radiation screened to an acceptable level.

The power supply 12 provides means for applying oppositecharges to the outer tubular member 16 and the inner tubular member 18, as shown particularly in FIG- URE 4. The power supply is connected to a suitable source of power such as 115 volts A.C. by a cord 51. An on-otf switch 52 is provided for turning the power on and off. A lamp 53 is provided for indicating whether the power supply is turned on or off. A fuse holder 54 is provided. The A.C. power is connected to a transformer 56 which reduces or increases the voltage to the desired voltage. The output of the transformer is rectified by a bridge type rectifier 57 which supplies its outa put to conductors 58 and 5?. The polarity on these conductors can be reversed by the reversing switch 61. The conductors 55 and 59 are carried in a cable 62 and con: nect the power supply to the ion generating assembly 14.

This cable also carries conductors 63 and 64 for energizing the fan motor 34.

The cables 51 and 62 can be removed and stored in the space 66 provided within the carrying case 11. The ion generating assembly 14 can be lifted into the space 13 by using handles 67 provided on the outer tubular member 16. a e i From the foregoing, it can be seen that the power supply serves as means for providing a charge of opposite polarities to the outer and inner tubular members 16 and 18 to thereby establish an electrostatic field between the members as shown particularly in FIGURE 4. A radial field is established between the outer and inner tubular members 16 and 18, as shown, which turns into a fringing field at the forward opening of the inner tubular member and in the area in which the radiationtrap 46 is located.

Operation of our ion generator in performing our method may now be briefly described as follows. Let it be assumed that a negative charge has been applied to the inner tubular member 18 and that a positive charge has been applied to the outer tubular member 16. Also let it be assumed that the radioactive source is Krypton 85. Krypton 85 radiates hard beta, gamma and secondary gamma rays (often called bremsstrahlung). The

primary radiation from the Krypton 85 source is hard effectively increases the usable ionization path of the hard beta particles in comparison to the normalpath length from the emitter to the electrode 18, and for that reason considerably enhances the effectiveness of the radiated hard beta particles from the radioactive source. Since the usable ionization path is substantially increased by reflection for the hard beta particles, it is readily apparent that the quantity of ions created in the inner tubular member 18 is substantially increased to greatly increase the efficiency of Krypton 85 as an ionization source.

The direct gamma radiation from the Krypton 85 source is attenuated to an acceptable level by the lead shielding provided by the inner cylindrical member 18. As the ions are generated in the inner tubular member, they are urged forwardly by the wind or air passing through the inner tubular member. Until they reach the forward end of the tubular member 18, they are not affected by the electrostatic field betwen the members 16 and 18. However, as they approach the forward end of the inner tubular member 18, they pass into the fringing field hereinbefore described. At the same time, they pass through the holes provided in the radiation trap 46.

Because of the polarities chosen, the positive ions as they pass into the fringing fields are attracted by the inner tubular electrode 13 and are collected thereby. The negative ions, on the other hand, travel in the opposite direction towards the positive tubular electrode 16. However, their travel is interrupted by the air flow passing through the tubular members 16 and 13 which carries them out towards the position Where they are required. It is readily apparent that positive ions can be obtained from the device merely by reversing the polarities.

The radiation from the radioactive source appearing outside of the ion generator structure itself is attenuated sufficiently so that it is well within levels readily acceptable to licensing authorities such as the Atomic Energy Commission. The direct gamma radiation, for example, is attenuated to an acceptable level by the lead shielding formed by the inner tubular member 13. The metal cones 31 also serve to reduce the direct gamma radiation and prevent it from passing out through the ends of the ion generating apparatus. Any remaining hard beta, beta scatter (electron multiplication) and secondary gamma attempting to pass through the ends of the ion generating apparatus is absorbed or attenuated to acceptable levels by the beta trap 46 at one end and by the fan 33 at the other end. The beta trap, as hereinbefore explained, is constructed in such a manner that only an accepted level of radiant flux can pass through the holes. The fan blades 36 of the fan, as pointed out previously, are also constructed to completely cover the rear end of the device to keep the primary and secondary radiation at this end of the device down to an acceptable level.

The above apparatus provides a very efficient apparatus for the generation of very large quantities of ions of the desired sign. It is believed that this is primarily made possible because of the use of the inner tubular member formed of a relatively high density material which causes reflection of the hard beta particles to increase the path of travel of the hard beta particles and to thereby greatly increase the amount of ionization which can be caused by the radiation from a Krypton source and to thereby greatly build up an ion plasma in a relatively confined space. The apparatus makes possible the use of relatively inexpensive source of radiation, while at the same time making its use very safe. The combination of the inner tubular member of relatively high density material and the outer tubular member of relatively low density material minimizes the creation of secondary radiation. The high density material serves to reflect, whereas the low density material serves to minimize secondary radiation production by the primary radioactive rays.

Krypton 85 is a particularly effective radiation source because it is'an inert gas and large quantities can be in troduced into a simple eifective device having any desired configuration which is selected to provide the most etlicient source, while at the same time giving the least it? interference to air flow through the device in which it is used. If a rupture of the source should occur, the inert low toxicity gas is simply dissipated into the surrounding air and is rapidly diluted to such an extent that there is no danger. Such would not be the case with solid emitters.

It has been found that certain dimensions of the apparatus are relatively critical. For example, in one embodiment of the invention, the following dimensions were utilized:

Outer tubular member 16-outside diameter 8.0 inches;

inside diameter 7.935 inches; length 28 inches Inner tubular member Iii-outside diameter 5.50 inches;

inside diameter 4.94 inches; length 14 inches Cone shields 31maximum diameter of 2 inches Beta. trap:

i=1 inch d=0.l85 inch A=11.l1 sq. in. 0:8.04 sq. in. 9:213

A voltage of 1600 volts D.C. was applied to the outer tubular member 16. With a wind velocity of 800 feet per minute, it was found that 6.24 l0 negative ions per second were collected.

It should be pointed out that the above dimensions and figures are only representative. The primary criteria is that the shielded ion or plasma chamber and associated structures should be so designed that the maximum advantage is taken out of back-scattering of the radiation with the minimum efiect on the desired air fiow pattern. Thus, the shape and size of the members 16 and 18 is involved. The size and shape of the supporting blocks, the shielding cones 31 and the like are also important so that turbulence within the device is reduced to a minimum. The size of the shields, of course, depends upon the size of the radiation source. The radiation traps must be con structed in such a manner that they function and still do not produce undue back pressure within the device. When the fan is an integral part of the device, the fan blades should be formed of heavy enough material and should be arranged in such a manner that they provide adequate shielding. The fan at the same time must provide the proper air flow through the apparatus, while at the same time keeping turbulence at a minimum.

In certain applications of our ion generator we have found it desirable to provide another embodiment which is shown in FIGURE 6 which is particularly useful in the elimination of the static charges of electricity. This is particularly true where a high concentration of ions of one sign is required in a relatively small space to accomplish the desired control to prevent a static charge buildup. In certain cases, the diffusion of the ion cloud blown from certain devices may be such that the effective density of the desired ions is reduced below the point where control of the static charge build-up can be maintained. When such is the case, it is desirable to focus the ion cloud on the process or on the articles on which it is desirable to control the static charge build-up to thereby increase the ion density and ensure control of the static build-up.

When it is possible to bring the ion generating apparatus into close proximity to the process, the utilization of radioactive foil such as radium and polonium 210 has been somewhat successful because they provide a cloud of ions in relatively close proximity thereto which is extremely dense. However, such sources pose numerous problems in certain processes and applications where it is impossible to bring the ion generator into close proximity to the problem area. Apparatus particularly used for such purpose is shown in FIGURE 6 and consists of a radioactive source 71 of a suitable material such as Krypton 85. The Krypton 85 is encapsulated in a long hermetically sealed tubular member of a suitable low assailed density material such as aluminum. This tubular source 71 is mounted within a cylindrical shield 72 of suitable material with an atomic number above 25 and supported therein by 'blocks 73. The cylindrical shield 72 is provided With an elongate slot '76 which extends substantially for the entire length thereof. This shield is in the form of a beta shield similar to that hereinbefore described in the embodiment shown in FIGURES 1 through 5. The cylindrical member is provided with ends 74 which also serve as a shield.

Since the ion emission from the ion generating apparatus shown in FIGURE 6 is normally diiiuse, it is desirable in certain applications to increase the ion concentration in a work area as, for example, the work area represented by the box 81. This is accomplished by placing a metal target 82 on the other side of the area 81 opposite the slot 74 and is grounded as shown. Shield 72 is also grounded and a high positive D.C. v'oltage is applied to the radioactive source to establish an electric field between the shield and the source. A field is also established between the target 82 and the radioactive source 71. The target 82 serves to attract the desired ions, whereas the undesired ions are attracted to and collected by the source when they return to the power supply and suppressed. A source of compressed air (not shown) can be introduced into the chamber formed by the shield 72 to help eject the desired ions.

From the foregoing, it can be seen that the desired ions are, therefore, attracted into the problem area with little or no difiusion so that it is possible to control th charge build-up within the area 81.

It is apparent from the foregoing that we have provided a new and improved ion generator and method which is particularly adapted for creating large quantities of ions of the desired sign efiiciently and in suiiicient quantities so that the device can be used in many industrial applications for controlling the build-up of static charges. that they are readily acceptable under present day safety standards.

We claim:

1. in an iongenerator for creating an excess of ions of one sign, a radioactive source, a member of high density material surrounding said radioactive source and spaced from the source, the spacing between said radioactive source and said member of high density material being substantially less than the normal distance of travel of the radioactive rays from said source so that said rays strike said member of high density material and are backscattered therefrom, said rays causing the creation of a substantial number of positive and negative ions in the an in the vicinity of said radioactive source, a member of low density material surrounding said member of high density material, means for applying the'charge of one s gn to one of said members and a charge of theopposite sign to the other of said members to establish an electrostatic field between said members for separating the desired ions from the undesired ions.

2. in an ion generator for creating an excess'of ions of one sign, a member of low density material having open ends, a member of high density material having open ends and being disposed within said member of low density material, a radioactive source mounted within said member of high density material, the spacing between the member of high density material and the radioactive source being less than the normal distance of travel of the radioactive rays from said source so that said rays impinge upon said member of high density material, said member of high density material causing back-scattering of said rays so that said radioactive rays cause the creation of a substantial number of positive and The radiation levels from the device are such negative ions in the air within said member of high density material, means for applying a charge of one sign to one of said members and a charge of the opposite sign to the other of said members to establish an electrostatic S field between said members for separating the desired ions from the undesired ions, and means mounted in both of said members for inhibiting the escape of radioactive rays from all of the open ends of said members.

3. An ion generator as in claim 2 wherein said means for inhibiting the escape of said rays includes a trap in the form of a plastic member mounted in one end of one of said members, said plastic member having a plurality of holes therein axially aligned with the path of flow of the air through the member in which it is mounted, the thickness of said member being such that the angle of incidence of said rays prevents escape of the radioactive rays.

4. In an ion generator for creating an excess of ions of one sign in air, a radioactive source, a member of high density material surrounding said radioactive source, the spacing between said radioactive source and said member of high density material being less than the normal distance of travel of the rays from said source so that the rays are back-scattered from said member of high density material, said rays causing the formation of ions of both signs in the air, said member being formed with an opening for the escape of ions, a radiation trap mounted in said opening for preventing radioactive rays from passing from said opening, said radiation trap being formed with a plurality of holes to permit the ions to pass therethrough and means for establishing an electrostatic field in said opening to cause separation of the desired ions from undesired ions.

5. An ion generating device as in claim 4 together with a target independently mounted remote from the member and wherein said electrostatic field is established between the target and said member.

6. An ion generator comprising a radioactive source having a substantial radiation of hard beta particles, and means disposed about and spaced from said radioactive source and forming an ionization zone between itself and said radioactive source, the spacing between said means and said radioactive source being substantially less than the normal distance of travel of the hard beta particles, said means being of a high density material whereby the hard beta particles impinge upon and are back-scattered into said ionization zone.

7. An ion generator as defined in claim 6 wherein said means disposed about the radioactive source comprises 9. An ion generator as defined in claim 6 together with means for creating an electric field in at least a portion of said ionization zone for separating desired ions from undesired ions.

10. An ion generator as defined in claim 6 together with means for passing air through said ionization zone to carry ions out of the ion generator. 7

V 11. An ion generator as defined in claim 6 together with target means spaced from said first means, and a source of potential connected between said target and,

said first means to create an electrostatic field to focus 7 ions toward the target.

12. An ion generator comprising a radioactive source having a substantial radiation of hard beta particles, first means disposed about and spaced from said radioactive source and forming anionization zone between itself and said radioactive source, the spacing between said first j 7 means and said radioactive source being less than the normal distance of travel or the hard beta particles, said first means being of a high density material whereby the hard beta particles impinge upon and are back-scattered from said first means into said ionization zone, and second means disposed about both said radioactive source and said first means, said second means extending beyond said first means and a source of potential connected between said first and second means whereby an electric field is produced in said ionization zone.

13. In an ion generator for creating an excess of ions of one sign, a member of low density material having open ends, a member of high density material having open ends and being disposed within said member of low density material, a radioactive source mounted within said member of high density material, the spacing between the member of high density material and the radioactive source being less than the normal distance of travel of the radioactive rays from said source so that said rays impinge upon said member of high density material, said member of high density material causing back-scattering of said rays so that said radioactive rays cause the creation of a substantial number of positive and negative ions in the air within said member of high density material, and means for applying a charge of one sign to one of said members and a charge of the opposite sign to the other of said members to establish an electrostatic field between said members for separating the desired ions from the undesired ions, said radioactive source being in the form of a cylindrical member, and means mounted on opposite ends of said cylindrical member having a diameter substantially greater than the diameter of the cylindrical member to provides a shield from the radiation from said radioactive member.

14. In an ion generator comprising a radioactive source having a substantial radiation of hard beta particles, first means disposed about said radioactive source and forming an ionization zone between itself and said radioactive source, the spacing between said first means and said radioactive source being less than the normal distance of travel of the hard beta particles, said first means being of a high density material whereby the hard beta particles impinge upon and are back-scattered from said first means back into said ionization zone, and second means disposed about both said radioactive source and said first means, said second means extending beyond said first means and a source of potential connected between said first and second means whereby an electric field is produced in said ionization zone, said first means being a tube of high density material and said second means being a tube of low density material, the first means providing a surface for back-scattering and multiplication of the hard beta particles and the second means minimizing secondary radiation to the outside of the generator, and a fan disposed at one end of said tube of low density material and adapted to force air through both of said tubes, said fan including overlapping blades of low density material, said blades having a diameter only slightly less than the inner diameter of said tube of low density material to inhibit the escape of primary radiation, and shielding means of low density material disposed within said tube of high density material and in axial alignment therewith, said shielding means including members located on opposite ends of said radioactive source.

15. In an ion generator for generating an excess of ions of one sign, a member of lew density material having open ends, a member of high density material having open ends and being disposed within said member of low density material, a radioactive source mounted within said member of high density material, the spacing between the member of high density material and the radioactive source being less than the normal distance of travel of the radioactive rays from said source so that said rays impinge upon said member of high density material, said member of high density material causing back-scattering of said rays so that said radioactive rays cause the creation of a substantial number of positive and negative ions in the air within said member of high density material, means for applying a charge of one sign to one of said members and a charge of the opposite sign to the other of said members to establish an electrostatic field between said members for separating the desired ions from the undesired ions, a fan mounted on one end of said member of low density material, said member of low density material having a length substantially greater than the length of the member of high density material, said high density member having an open end facing the fan, said fan being provided with overlapping blades of substantially uniform low density material to inhibit the escape of primary and secondary radiation.

References Cited by the Examiner UNITED STATES PATENTS 1,956,590 5/34 Pressler 250-237 2,346,864 4/44 Packard 250-237 2,756,840 7/56 Maas 250-44 2,785,312 3/57 Martin 250-44 2,928,941 3/ Hicks et al. 250-44 2,939,006 5/60 Oswald 250-44 RALPH G. NILSON, Primary Examiner. 

1. IN AN ION GENERATOR FOR CREATING AN EXCESS OF IONS OF ONE SIGN, A RADIOACTIVE SOURCE, A MEMBER OF HIGH DENSITY MATERIAL SURROUNDING SAID RADIOACTIVE SOURCE AND SPACED FROM THE SOURCE, THE SPACING BTWEEN SAID RADIOACTIVE SOURCE AND SAID MEMBER OF HIGH DENSITY MATERIAL BEING SUBSTANTIALLY LESS THAN THE NORMAL DISTANCE OF TRAVEL OF THE RADIOACTIVE RAYS THEN THE NORMAL DISTANCE OF TRAVEL STRIKE SAID MEMBER OF HIGH DENSITY MATERIAL AND ARE BACKSCATTERED THEREFROM, SAID RAYS CAUSING THE CREATION OF A SUBSTANTIAL NUMBER OF POSITIVE AND NEGATIVE IONS IN THE AIR IN THE VINCURITY OF SAID RADIOACTIVE SOURCE, A MEMBER OF LOW DENSITY MATERIAL SURROUNDING SAID MEMBER TO HIGH DENSITY MATERIAL, MEANS FOR APPLYING THE CHANGE OF ONE SIGN TO ONE OF SAID MEMBERS AND A CHARGE OF THE OPPOSITE SIGN TO THE OTHER OF SAID MEMBERS TO ESTABLISH AN ELECTROSTATIC FIELD BETWEEN SAID MEMBERS FOR SEPARATING THE DESIRED IONS FROM THE UNDERSIRED IONS.
 6. AN ION GENERATOR COMPRISING A RADIOACTIVE SOURCE HAVING A SUBSTANTIALLY RADIATION OF HARD BETA PARTICLES, AND MEANS DISPOSED ABOUT AND SPACED FROM SAID RADIOACTIVE SOURCE AND FORMING AN IONIZATION ZONE BETWEEN ITSELF AND SAID RADIOACTIVE SOURCE, THE SPACING BETWEEN SAID MEANS AND SAID RADIOACTIVE SOURCE BEING SUBSTANTIALLY LESS THAN THE NORMAL DISTANCE OF TRAVEL OF THE HARD BETA PARTICLES, SAID MEANS BEING OF A HIGH DENSITY MATERIAL WHEREBY THE HARD BETA PARTICLES IMPINGE UPON AND ARE BACK-SCATTERED INTO SAID IONIZATION ZONE. 